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Liverpool, 30, was ordered held without bail. She appeared unruffled by the charges during Tuesday's brief proceeding. Authorities have described her as emotionally disturbed, but her lawyer, Mathew Mari, said she had declined to give him any details on her medical history.

"She's adamant that she did not confess and that she's not guilty" and didn't want to discuss anything else, Mari said.

Authorities said Liverpool and Watton were talking or arguing on a platform at the 42nd Street-Seventh Avenue station around 1 p.m. Monday before Liverpool pushed Watton in front of an approaching train. She was found dead under it, and Liverpool was apprehended within minutes.

"This is a strong case, with multiple eyewitnesses" and an admission from Liverpool, Manhattan Assistant District Attorney Matthew Thiman said.

Police said they were looking at video surveillance to try to determine what led to the attack.

Liverpool, who lives in Queens, worked as a health aide until about three weeks ago, Mari said. He didn't know how her job had ended.

A phone message left at Watton's home went unanswered Tuesday afternoon.

Law enforcement officials say Liverpool previously claimed to police she had shoved another person in front of an oncoming train at Union Square station on Oct. 19.

At the time, police did not find her claim credible; two different witnesses told investigators the victim had jumped in front of the train and treated the death as a suicide, officials said.

Now the NYPD is reexamining the subway death, law enforcement officials said.

Subway deaths from pushes are not common, but there have been a few in the past few years. In 2014, Kevin Darden, 34, was charged with killing a 61-year-old immigrant from Hong Kong, Wai Kuen Kwok, by shoving him into the path of a subway train in the Bronx. He pleaded guilty to manslaughter and is awaiting sentencing.

In 2012, Erika Menendez, a mentally ill woman who had a history of attacking strangers, shoved an immigrant from India off a subway platform in Queens. She pleaded guilty to manslaughter and was sentenced to 24 years in prison. The victim, Sunando Sen, was 46.

Also in 2012, a homeless man, Naeem Davis, was arrested and charged with shoving Ki-Suck Han, a Korean immigrant, into the path of a subway train at a station near Times Square.

A fatal subway push in 1999 led to a state law, known as Kendra's Law, that allows supervision of certain patients outside of institutions to make sure they're taking medications and don't present a public safety threat. It came after the death of Kendra Webdale, who was pushed to her death by a former mental patient.